New Scientist - USA (2022-02-19)

48 | New Scientist | 19 February 2022

millennia old, there are few of them and they

aren’t exactly thriving. This doesn’t, however,

mean that nothing survives. In a 2007 study,

researchers managed to grow bacteria from

Antarctic ice that was up to 8 million years

old. Fortunately, those that endured weren’t

ones that make people ill. Indeed, bacteria that

infect humans are adapted to live at our body

temperatures, so it is highly unlikely that they

would survive for long periods below zero.

The same is true for fungi. Some 300 fungi

are known to be pathogenic to humans,

including Cryptococcus neoformans, which

can cause dangerous lung infections. Fungi

have been found in ice, from Greenland and

Svalbard in the north to Antarctica in the

south, and in the slush left behind when

glaciers retreat. What’s more, ice from

Antarctica has yielded fungi that can be grown

in the lab. But again, the quantities are tiny and

they weren’t species that are dangerous to us.

This pattern holds for glacier ice too, even

though it is often younger and less cold than

ice sheets. “Glaciers are the cleanest places on

Could melting ice and

permafrost expose us to

disease organisms that infected

now-extinct ancestral human

groups? It is a dramatic idea,

but not an impossible one.

Neanderthals and Denisovans

were closely related to us and

it is likely that early modern

humans were afflicted by

some of the same pathogens,

including those that cause the

common cold and cold sores.

A tiny quantity of bacteria or

viruses in melting ice wouldn’t

pose a significant risk. The

real danger would come if a

well-preserved body thawed

out of permafrost and released

lots of infectious material.

That seems unlikely. Although

Denisovans lived in Siberia and

Tibet, their known remains are

very sparse and, to date,

include nothing more

substantial than a jawbone.

Neanderthal remains are

numerous, but they come

mostly from far outside the

permafrost zone. Besides, no

bodies with preserved flesh

have yet been found.

That said, we can’t rule it

out. In 2016, a mummified

wolf pup was found in thawing

permafrost in Canada, and it

turned out to be 57,000 years

old. Neanderthals are thought

to have survived until around

40,000 years ago and

Denisovans until about

50,000 years ago. So it is

possible a frozen hominin

corpse is out there somewhere

waiting to emerge from the

freezer.

Neanderthal colds

and Denisovan flu

reassuring. And, although an analysis of very

salty Arctic water found plenty of viruses, the

majority specialised in infecting bacteria and

posed no risk to people. Similarly, last year

Thompson’s group identified a range of viruses

in ice cores from Tibet, where the ice was as

much as 15,000 years old. The majority were

infecting bacteria. “On the warmer glaciers,

you can have microbes and viruses growing on

the surface,” says Thompson. The bacteria are

species that can survive in the cold, and the

viruses parasitise them. “It’s an ecosystem.”

Compared with bacteria, there have been far

fewer studies of viruses in ice. But we do know

that they are blown there by the wind, and also

that viruses are only contagious when present

in large numbers. Vick-Majors finds these facts

heartening. “There could be a couple of human

pathogens in that package of air that landed

there,” she says. “I just wouldn’t expect there

to be enough of them to be a threat.”

Even if microorganisms being released

from glaciers and ice sheets are unlikely to

make us ill, they aren’t completely innocuous.

“They’ll be going into river systems,” says

Karen Cameron at the University of Glasgow,

UK. “They’re going to be buried within

build-up of sediments and organic matter

in lakes and downstream fjord environments

and near-shore environments.” She has shown

that meltwater from the Greenland ice sheet

carries microbes far downstream, and that

such microbes may well remain active in their

new homes. Many of these organisms are rare,

so they aren’t well studied, and it is hard to

predict what they will do. “We really don’t have

a sense of how the ecology is going to change

and what are the consequences of that

ecological change,” says Cameron.

Nevertheless, at this point, you may be

wondering why the US National Academies are

worried about diseases emerging from frozen

regions. The thing is, while ice is pretty safe,

permafrost isn’t. Organic matter such as soil

is a much more congenial environment for

pathogenic microbes, so permafrost is likely

to contain all sorts of nasties. The 2016 anthrax

outbreak in Russia is just one example.

Human remains exhumed from frozen

ground in Alaska have yielded the complete

this planet,” says Lonnie Thompson at Ohio

State University, who has spent decades

exploring these rivers of ice. “When we’re

in the field, we drink the meltwater from

those glaciers. To date, none of our field team

has had any issues from drinking that water.”

Viruses in the freezer

So it looks as if we needn’t worry too much

about such microbial life emerging from

ice sheets and glaciers. But what about

viruses, those tiny structures that are only

ambiguously alive?

In 1999, researchers identified a virus

that infects tomatoes and other plants in

140,000-year-old glacier ice from Greenland.

Five years later, a second group suggested that

ice might act as a reservoir for pathogenic

viruses including influenza A, caliciviruses

that cause gastroenteritis, and certain

enteroviruses (the group that includes

the polio virus). There was little evidence to

back up this idea and other studies are more

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